Catalytic conversion system



Dec. 9, 1958 w. MCCLURE I 2,363,827

CATALYTIC CONVERSION SYSTEM Filed Aug. 19, 1953 Elevator Re generatorINVENTOR. WILLIAM L. M CLURE l7 rL-+O. Sdwm ATTORNEY United StatesPatent '0 2,863,827 CATALYTIC CONVERSION SYSTEM William L. McClure,Toledo, Ohio, assignor to Sun Oil :(Eompany, Philadelphia, Pa., acorporation of New ersey Application August 19, 1953, Serial No. 375,1103 Claims. (Cl. 208-165) This invention relates to processes for theconversion of hydrocarbon material by contact with a granular contactmaterial and more particularly to a method for introduction of granularcontact material into a hydrocarbon conversion zone.

In hydrocarbon conversion systems of the moving bed type, it iscustomary to gravitate the granular contact material, e. g. crackingcatalyst, as a compact mass from a supply hopper through a confinedelongated zone known as the seal leg and thence into the hydrocarbonconversion zone. The latter is generally maintained at a higher pressurethan that in the supply hopper and the length of the seal leg must besufficiently great to provide a vertical head of catalyst in the sealleg to overcome this pressure differential.

Since the hydrocarbon conversion zone is generally maintained at arelatively high pressure, there is a tendency for hydrocarbon vapors topass upwardly from the hydrocarbon conversion zone through the seal leg.In order to prevent excessive escape of hydrocarbon vapors in thismanner, it is customary to introduce a sealing gas, for example, steam,into a sealing zone above the hydrocarbon conversion zone and adjacentthe lower end of the seal leg. The sealing gas passes upwardly throughthe seal leg and prevents the hydrocarbon vapors from passing upwardlyout of the hydrocarbon conversion zone to an excessive extent.

In using steam as a sealing gas in a process employing a granularcatalyst, for example a clay catalyst, which has substantial ability toadsorb steam at the temperatures commonly employed, a problem arisessince the sealing steam tends to become adsorbed by the catalyst and tobe unable, therefore, to eflectively perform its function of maintainingthe desired pressure gradient across the seal leg. It is important forproper operation that a uniform decrease in pressure be maintained asthe steam passes upwardly through the seal leg. In prior art operation,however, this has not been obtained since, as the steam enters thebottom of the seal leg, substantial amounts thereof become adsorbed onthe catalyst with the result that the pressure at levels higher in theseal leg is disadvantageously low and a large pressure gradient occursnear the bottom of the seal leg. This large pressure gradient causes adanger of interference with or stoppage of the flow of catalyst throughthe seal leg.

Previously attempts have been made to overcome this problem by hydratingthe catalyst before it enters the seal leg, for example by introducingsteam into the hopper from which the seal leg receives the catalyst.This method has not been completely successful, however, since it isdifficult to obtain good enough distribution of steam throughout thecatalyst in the hopper to obtain complete saturation with steam and alsobecause, even if substantially complete saturation is obtained in thehopper, a large pressure gradient still occurs at the bottom of the sealleg.

According to the present invention, the disadvantages "ice of prior artoperation are overcome by introducing steam into the seal leg itself ata level intermediate of the ends of the seal leg. It has been found thatsuch operation eliminates any excessive pressure gradient at the bottomof the seal leg.

The introduction of steam into the seal leg itself serves to maintainthe contact material more nearly saturated with steam during its passagethrough the seal leg. Since the pressure increases as the catalyst flowsdownwardly through the seal leg, the amount of steam vwhich the catalystis capable of adsorbing increases as the catalyst flows downwardly.Therefore, unless steam is introduced into the seal leg, catalyst whichis completely saturated at the top of the seal leg will be capable ofadsorbing considerably more steam at the bottom of the seal leg wherethe pressure is substantially higher; and such adsorption of steam atthe bottom of the seal leg causes a large pressure gradient. The presentinven tion provides catalyst which is more nearly saturated with steamat the bottom of the seal leg so that excessive adsorption of sealingsteam does not occur.

According to the present invention, steam can be introduced at one ormore vertical levels between the ends of the seal leg. Generally thegreater the number of points of introduction of steam, the more uniformwill be the degree of saturation of the catalyst as-it flows downwardlythrough the seal leg. By maintaining a .more uniform degree ofsaturation the advantageous result is obtained of maintaining a moreuniform rate'of pressure increase as the catalyst moves downwardlythrough the seal leg, since the steam which passes upwardly from thesealing zone through the seal leg is substantially all employed in thecreation of a pressure gradient rather than being adsorbed in part bythe catalyst.

The invention will be further described with reference to the attacheddrawing which is a schematic representation of apparatus in which theprocess of the invention may be performed. In the drawing there areshown a hydrocarbon conversion vessel or reactor .10, a regenerationvessel 11, elevating means 12 for conveying solids after removal fromthe regenerator 11 upwardly to a level above the hopper 13 which issituated above reactor 10. A seal leg 14 extends downwardly from hopper13 to reactor 10.

In operation granular solids are gravitated downwardly through thehydrocarbon conversion zone 15 within reactor 10 and are contactedtherein with hydrocarbon materials introduced through means not shown toeffect conversion thereof. The catalyst is then gravitated through line16, into regenerator 11 through which it gravitates as a compact mass.In regenerator 11, the catalyst is contacted with combustion supportinggas introduced through means not shown in order to effect combustion ofthe carbonaceous materials contained on the catalyst, such materialshaving been deposited thereon during the-preceding hydrocarbonconversion operation. The catalyst is then gravitated through line 17into the elevating means 12 which may be of any suitable type, forexample a bucket elevator or a pneumatic elevator of known type. Fromthe upper end of elevating means 12 the catalyst is introduced intoconduit 18 and passed therethrough into hopper 13.

The catalyst in hopper 13 is at an elevated tempera ture, for exampleabout 700 F., and as originally introduced thereinto is in asubstantially dehydrated condition, having become dehydrated in theregenerator because of the high temperature and low partial pressure ofsteam therein. In order to hydrate the catalyst, steam is introducedinto hopper 13 through line 19. The hydrated catalyst is withdrawn fromhopper 13 through line 14 and travels through the latter as a compactmass.

The pressure inhopper 13 is relatively low, for example atmosphericpressure, whereas the pressure in the sealing zone 20 into which sealleg 14 discharges is relatively high, for example lOp. s. i. g. In orderto maintain the catalyst substantiallyzsaturated with steam during itspassage through seal leg 14, steam is introduced into the latter throughlines 21 and 22. The steam thus introduced becomes adsorbed on thecatalyst and satisfies the increased capacity of the catalyst for steamas it travels downwardly through seal leg 14 at gradually increasingpressure.

Sealing steam is introduced into sealing zone 20 through line 23. Thissteam maintains sealing zone 20 at a somewhat higher pressure than thepressure in hydrocarbon conversion zone 15, thereby preventingsubstantial passage of hydrocarbon vapors upwardly from hydrocarbonconversion zone 15 into sealing zone 20. Part of the sealing steampasses upwardly from sealing zone through seal leg 14 into hopper 13.Since the catalyst is maintained substantially saturated with steamthroughout its passage through seal leg 14, the sealing steam is enabledto maintain a substantially uniform pressure gradient across the sealleg 14.

In contast to the operation described above, an operation wherein steamis not introduced through lines 21 and 22 is incapable of providing auniform pressure gradient across the seal leg 14. The sealing steam insuch operation as it enters the lower end of seal leg 14 comes incontact with catalyst which is not saturated with steam and substantialamounts of the sealing steam become adsorbed on the catalyst at thatpoint. Thus there is a large decrease in pressure of the sealing steamnear the lower end of the seal leg whereas in the operation describedaccording to the invention the sealing steam decreases in pressure onlygradually as it rises through the seal leg 14.

From the above it is seen that operation according to the inventionprovides a uniform flow of solids downwardly through the seal leg and auniform flow of sealing steam upwardly through the seal leg and thusminimizes or eliminates any tendency for nonuniform conditions tointerfere with or stop the flow of catalyst through the seal leg.

Although the invention has been described with reference to ahydrocarbon conversion catalyst. it is to be understood that it is alsoapplicable to inert, porous, contact material of the known types used inhydrocarbon conversion processes.

The invention claimed is:

1. In a process for conversion of hydrocarbons which comprisesintroducing porous granular hydrocarbon conversion supporting contactmaterial unsaturated with steam into a relatively expanded supply zone,gravitating contact material from said supply zone into and through anelongated relatively confined zone against gradually downwardlyincreasing pressure, gravitating contact material from said confinedzone into a sealing zone, introducing contact material from said sealingzone into a conversion zone, and contacting hydrocarbons with saidcontact material in said conversion zone under conversion conditions,the improvement which comprises: introducing steam into said supply zoneto substantially saturate said contact material with steam at thepressure in said supply zone; introducing additional steam into saidconfined zone to further increase the adsorbed steam content of saidcontact material, substantially all of the contact material which iscontacted with said additional steam being subsequently introduced intosaid sealing zone; introducing steam into said sealing zone; and passingsteam upwardly from said sealing zone into and through said confinedzone.

2. Method according to claim 1 wherein additional steam is introduced ata level approximately equidistant between the adjacent upper and lowerlevels of steam introduction.

3. Method according to claim 1 wherein additional steam is introduced ata plurality of levels intermediate the ends of said confined zone.

References Cited in the file of this patent UNITED STATES PATENTS2,410,309 Simpson et a1 Oct. 29, 1946 2,606,861 Eastwood Aug. 12, 19522,626,235 Wilson Jan. 20, 1953 2,631,123 Kaulakis Mar. 10, 19532,673,832 Lassiat Mar. 30, 1954

1. IN A PROCESS FOR CONVERSION OF HYDROCARBONS WHICH COMPRIESEINTRODUCING POROUS GRANULAR HYDROCARBON CONVERSION SUPPORTING CONTACTMATERIAL UNSATURATED WITH STEAM INTO A RELATIVELY EXPANDED SUPPLY ZONE ,GRAVITAING CONTACT MATERIAL FROM SAID SUPPLY ZONE INTO AND THROUGH ANELONGATED RELATIVELY CONFINED ZONE AGAINST GRADUALLY DOWNWARDLYINCREASING PRESSURE, GRAVITATING CONTACT MATERIAL FROM SAID CONFINEDZONE INTO A SEALING ZONE, INTRODUCING CONTACT MATERIAL FROM SAID SEALINGZONE INTO A CONVERSION ZONE, AND CONTACTING HYDROCARBONS WITH SAIDCONTACT MATERIAL IN SAID CONVERSION ZONE UNDER CONVERSION CONDITIONS,THE IMPROVEMENT WHICH COMPRISES: INTRODUCING STEAM INTO SAID SUPPLY ZONETO SUBSTANTIALLY SATURATE SAID CONTACT MATERIAL WITH STEAM AT THEPRESSURE IN SAID SUPPLY ZONE; INTRODUCING ADDITIONAL STEAM INTO SAIDCONTENT OF SAID CONTACT MATERIAL, THE ADOPTED STEAM CONTENT OF SAIDCONTACT MATERIAL, SUBSTANTIALLY ALL OF THE CONTACT MATERIAL WHICH ISCONTACTED WITH SAID ADDITIONAL STEAM BEING SUBSEQUENTLY INTRODUCED INTOSAID SEALING ZONE; INTRODUCING STEAM INTO SAID SEALING ZONE; AND PASSINGSTEAM UPWARDLY FROM SAID SEALING ZONE INTO AND THROUGH SAID CONFINEDZONE.